1. Field of the Invention
The invention relates to medical devices to assist an individual in passing kidney stones while preserving the urethral lining through which the stones pass.
2. Description of the Related Art
Kidney stones are one of the most painful urologic disorders and yet also one of the most common. In the year 2000 in the United States there were roughly 2.7 million doctor visits and outpatient hospital visits by adults aged 20 or older with “calculus of kidney and ureters” as a listed diagnosis (Litwin M S, Saigal C S. Introduction. In: Litwin M S, Saigal C S, editors. Urologic Diseases in America. DHHS, PHS, NIH, NIDDK. Washington, D.C.: GPO; 2007. NIH publication 07-5512:3-7). Men tend to be afflicted with kidney stones more than woman and the risk of a man developing kidney stones rises at forty years of age.
A stone is essentially a hard mass of crystals that precipitate out of and separate from the urine to build up on the inner surfaces of the kidney. In healthy individuals, chemicals in the urine inhibit the crystals from forming. In afflicted individuals, these chemical inhibitors do not work properly.
The stones are made up of various combinations of chemicals but the most common constituents are calcium with oxalate or phosphate. Struvite stones are a less common variety caused by a urinary tract infection. Bacteria such as proteus and klebsiella associated with urinary tract infections produce the ammonia which is a precursor to struvite stone formation. Even less common varieties of stones are uric acid stones and cystine stones. Uric acid stones result from a low volume of urine with a low pH. They are more likely to occur in chemotherapy patients, dehydrated individuals, and those with inflammatory bowel disorders. The formation of cystine stones is associated with urine with a high pH and a rare disease called Cystinuria most common in children and young adults.
Urolithiasis is the medical term used to describe stones occurring in the urinary tract while nephrolithiasis describes stones occurring in the kidneys. More specific terms exist to identify the position of the stone within the urinary tract (comprising two ureters, the bladder, and the urethra). For example, ureterolithiasis is used to describe kidney stones specifically in the ureter. The ureter is made up of two narrow tubes that carry urine from the kidney to the bladder. From the bladder, urine exits the body via the urethra.
There is a paucity of treatment options for individuals afflicted with kidney stones. Chemical treatment options are generally impractical because acidic chemicals powerful enough to dissolve the stones also severely damage and are toxic in the urinary system in which the stones reside.
Some of the most recent kidney stone removal assistance devices comprise wires that branch from strands into filaments to create a multi-filament collector. Stones enter the device at the proximal end through gaps between the strands (wires) and are then retained by the multi-filaments distal to the spaced strands. In contrast, according to the basket forceps design of the present invention stones enter at the distal end as the arms open and dilate the urethra to release the stone into the forceps grasp for removal. Once grasped, the stone(s) are retained at the proximal end (bottom of the “basket”) as the arms close. United States Patent No. (hereinafter “USP”) U.S. Pat. No. 6,780,193 (“Surgical extractor” by Leslie, et al.) assigned to Boston Scientific Corporation discloses such a device with wires, strands, and filaments. Since the wires that form spaced strands must be limited in thickness and number to permit stones to enter between them, they may not be strong enough to provide a retraction function as do the rigid arms of the basket forceps of the present invention.
Other variations of the branched wire concept involve strands with distal ends that connect to a web-like fabric porous material instead of branching into multiple filaments. For, example U.S. Pat. No. 3,472,230 (“Umbrella catheter” by Thomas Fogarty and unassigned) discloses an umbrella attached to the distal end of four sliding spring wires. Similarly, U.S. Pat. No. 4,790,812 (“Apparatus and method for removing a target object from a body passageway” by Hawkins, Jr. et al. and unassigned) discloses a parachute basket attached to four helically wound spring wires. Although the dilating basket forceps arms of the present invention could be springing, slidable, and/or helically wound, they can also be stiff and longitudinally fixed in position.
Other devices and techniques to remove kidney stones rely upon fragmentation and aspiration. U.S. Pat. No. 6,517,531 (“Medical suction device” by Liu, et al.) assigned to Scimed Life Systems, Inc. describes a dual-lumen elongated member with a first suction lumen for aspiration and a second laser fiber lumen for delivering energy to breakdown larger stones. In contrast, the present invention relies upon mechanical urethral dilation, mechanical agitation, and natural gravitational forces to remove the stones.
Other patents addressing the kidney stone problem have focused on filtering the stones from the urine and securely retaining the stones from the time of collection to the time of lab analysis. U.S. Pat. No. 6,389,609 (“Universal stone catcher urinal system” by Stephen Andritz and unassigned) and U.S. Pat. No. 5,772,644 (“Filter pouch for stone and tissue sample collection” by Bark, et al.) assigned to Microtek Medical, Inc. disclose examples of such a filtration and retention system. These systems have limited utility because they do not address the entire scope of the kidney stone problem. They focus on post-collection sample preservation but do nothing to encourage the release of more difficult stones or alleviate patient pain. A filtration and retention system could be used simultaneously with the present invention and be placed where the stones exit the urethra via the balloon sheath or the retrievable stent's smooth lining.
Accordingly, a system and method is needed to assist individuals in passing kidney stones that: (i) reduces pain, (ii) accelerates passage, (iii) permits urination during the stone collection process, (iv) preserves the urethral lining, (v) has a means to assist with the passage of particularly difficult stones that become lodged deep in the urethral lining, (vi) can remain in place until all stones have passed, and (vii) can be easily removed.